title: Bis(sulfonylimide)ruthenium(VI) porphyrins: X-ray crystal structure and mechanism of C-H bond amination by density functional theory calculations.
abstract: The X-ray crystal structure of [Ru(VI) (NMs)2 (tmp)] (Ms=SO2 - p-MeOC6 H4 ; tmp=5,10,15,20-tetramesitylporphyrinato(2-)), a metal sulfonylimide complex that can undergo alkene aziridination and C-H bond amination reactions, shows a Ru=N distance of 1.79(3) Å and Ru-N-S angle of 162.5(3)°. Density functional theory (DFT) calculations on the electronic structures of [Ru(VI) (NMs)2 (tmp)] and model complex [Ru(VI) (NMs)2 (por(0) )] (por(0) =unsubstituted porphyrinato(2-)) using the M06L functional gave results in agreement with experimental observations. For the amination of ethylbenzene by the singlet ground state of [Ru(VI) (NMs)2 (por(0))], DFT calculations using the M06L functional revealed an effectively concerted pathway involving rate-limiting hydrogen atom abstraction without a distinct radical rebound step. The substituent effect on the amination reactivity of ethylbenzene by [Ru(VI) (NX)2 (por(0) )] (X=SO2 -p-YC6 H4 with Y=MeO, Me, H, Cl, NO2 ) was examined. Electron-withdrawing Y groups lower the energy of the LUMOs of [Ru(VI) (NX)2 (por(0))], thus facilitating their interaction with the low-lying HOMO of the ethylbenzene C-H bond and hence increasing the reactivity of [Ru(VI) (NX)2 (por(0) )]. DFT calculations on the amination/aziridination reactions of [Ru(VI) (NSO2 C6 H5 )2 (por(0) )] with pent-4-enal, an aldehyde substrate bearing acyl, homoallylic, and allylic C-H bonds and a C=C bond, revealed a lower reaction barrier for the amination of the acyl C-H bond than for both the amination of the other C-H bonds and aziridination of the C=C bond in this substrate.
authors.affiliation: Department of Chemistry, State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Guo
authors.forename: Xiangguo
authors.initials: X
authors.lastname: Guan
authors.forename: Jie-Sheng
authors.initials: JS
authors.lastname: Huang
authors.forename: Wai-Man
authors.initials: WM
authors.lastname: Tsui
authors.forename: Zhenyang
authors.initials: Z
authors.lastname: Lin
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Che
keywords: CH activation; amination; density functional calculations; porphyrinoids; ruthenium